Ultrasonography is the surgeon’s main imaging investigation for thyroid disease, with additional modalities used to assess disease extent, invasion and recurrence.
Ultrasonography
•
Ultrasonography assesses the thyroid gland, its nodules and regional lymphatics.
•
Nodule number, size, shape, margins, vascularity and features such as microcalcifications help predict malignancy risk.
•
Regional lymphatics, particularly in the lateral neck, can be assessed accurately for metastatic deposits.
•
Ultrasound guidance improves the accuracy of fine-needle aspiration compared with free-hand techniques.
•
Ultrasonography is non-invasive, inexpensive and does not involve ionising radiation.
Limitations and cross-sectional imaging
•
Ultrasonography has limited visualisation of central neck nodes, particularly those behind the sternum. Detected metastatic disease therefore requires cross-sectional imaging for full staging.
•
A plain chest radiograph can often predict retrosternal extension, but advanced imaging is needed to define its extent before management.
•
Computed tomography (CT) is the modality of choice for most of these indications. Rapid acquisition reduces breathing artefacts and allows simultaneous assessment of the lung fields.
Invasive and recurrent thyroid cancer
•
Contrast-enhanced CT helps determine the extent of airway invasion in invasive primary thyroid cancer.
•
Magnetic resonance imaging (MRI)* is superior for determining prevertebral fascia invasion.
•
Positron emission tomography (PET)* has limited applications in thyroid disease but may be considered for recurrent thyroid cancer.
•
PET is particularly useful when recurrent disease does not concentrate iodine: fluorodeoxyglucose (FDG) uptake increases and lesions become PET-positive.